There is known a capacitively coupled plasma processing apparatus configured to generate plasma in a processing space between circular plate-shaped upper and lower electrodes arranged parallel to each other and to perform a required process on a substrate such as a semiconductor wafer (hereinafter, simply referred to as a “wafer”) by the plasma. In such a capacitively coupled plasma processing apparatus, plasma density corresponding to a central portion of the upper electrode or the lower electrode is increased, and plasma density distribution in the entire processing space tends to become non-uniform.
To solve the problem, the present inventors have proposed a plasma processing apparatus 115 as depicted in FIG. 10 (see, for example, Patent Document 1). In this plasma processing apparatus 115, an upper electrode is divided into an inner electrode 110 and an outer electrode 111 surrounding the inner electrode 110. High frequency powers are independently applied to the inner electrode 110 and the outer electrode 111, and an electric field in a processing space (hereinafter, referred to as an “inner space”) corresponding to the inner electrode 110 and an electric field in a processing space (hereinafter, referred to as an “outer space”) corresponding to the outer electrode 111 are also individually controlled. Further, permanent magnet rows 112 to 114 are concentrically arranged on a top surface of the upper electrode about the center of the upper electrode, and a magnetic field is generated at a desired position within the processing space.
In this plasma processing apparatus 115, by individually adjusting the electric field in the inner space and the electric field in the outer space, plasma density in the inner space and plasma density in the outer space are independently controlled.
Further, in the plasma processing apparatus 115, circular ring-shaped magnetic force lines 116 and 117 concentrically distributed about the center of the upper electrode are respectively generated between the permanent magnet rows 112 and 113 and between the permanent magnet rows 113 and 114. Magnetic fields generated by these magnetic force lines 116 and 117 are formed in the inner space and in the outer space, and electrons within the inner space and the outer space are drifted by a Lorentz force in directions orthogonal to the magnetic force lines 116 and 117 (in the drawing, marks such as ‘●’ indicate drift directions of the electrons). At this time, the electrons drifted by the Lorentz force revolve around the center of the upper electrode at the vicinity of the surface of the upper electrode. The revolving electrons collide with molecules and atoms of a processing gas, and thus, plasma is generated. As a result, circular ring-shaped plasma distributed about the center of the upper electrode can be generated so as to correspond to the magnetic field.
In this plasma processing apparatus 115, the plasma density in the inner space and the plasma density in the outer space are independently controlled, and a multiplicity of circular ring-shaped plasma is generated. As a result, plasma density distribution in the entire processing space can be effectively controlled.
Patent Document 1: Japanese Patent Laid-open Publication No. H10-152775
However, the present inventors have conducted researches repeatedly and found out that the conventional plasma processing apparatus has the following issues. The magnetic field generated in the processing space has a horizontal component parallel to the upper and lower electrodes and a vertical component perpendicular to the upper and lower electrodes. The horizontal component is effectively used for controlling the plasma density within the processing space by individually controlling the electric field and the magnetic field. However, the vertical component complicates the relationship between the magnetic field and the electric field in the processing space, and the plasma density distribution in the processing space may not be controlled.